I. Field
The following description relates generally to communication systems, and more particularly to methods and apparatuses for scheduling uplink request Spatial Division Multiple Access (RSDMA) messages in an SDMA capable wireless LAN.
II. Background
In order to address the issue of increasing bandwidth requirements that are demanded for wireless communications systems, different schemes are being developed to allow multiple user terminals to communicate with a single access point by sharing the channel resources while achieving high data throughputs. Multiple Input or Multiple Output (MIMO) technology represents one such approach that has recently emerged as a popular technique for the next generation communication systems. MIMO technology has been adopted in several emerging wireless communications standards such as the Institute of Electrical Engineers (IEEE) 802.11 standard. IEEE 802.11 denotes a set of Wireless Local Area Network (WLAN) air interface standards developed by the IEEE 802.11 committee for short-range communications (e.g., tens of meters to a few hundred meters).
In communication systems, Medium Access Control (MAC) protocols are designed to operate to exploit several degrees of freedom offered by the air link medium. The most commonly exploited degrees of freedom are time and frequency. For example, in the IEEE 802.11 MAC protocol, the time degree of freedom is exploited through the CSMA (Carrier Sense Multiple Access). The CSMA protocol attempts to ensure that no more than one transmission occurs in a neighborhood of potential high interference. The frequency degree of freedom can be exploited by using different channels.
Recent developments have led to space dimension being a viable option. Spatial Division Multiple Access (SDMA) can be used for improving utilization of the air link by scheduling multiple terminals for simultaneous transmission and reception. Data is sent to each of the terminals using spatial streams. For example, with SDMA, a transmitter forms orthogonal streams to individual receivers. Such orthogonal streams can be formed because the transmitter has several antennas and the transmit/receive channel consists of several paths. The receivers may also have one or more antennas, such as in MIMO or Single Input-Multiple Output (SIMO) antenna systems. In one example, the transmitter may be an access point (AP) and the receivers may be stations (STAs). The streams are formed at the AP such that a stream targeted at a particular STA, for example, may be seen as low power interference at other STAs, which will not cause significant interference and not be ignored.
It is desirable that the process of scheduling uplink SDMA transmissions by each STA during each uplink SDMA transmission cycle, or epoch, be performed in a manner so as to ensure fair access by all the STAs to the network medium for data transmission. Simultaneously, given that certain types of data, such as voice over IP or streaming multimedia, requires a certain priority of transmission, it is desirable that the AP schedules uplink SDMA transmissions such that any Quality of Service (QoS) levels are maintained. Further, it is also desirable that the scheduling does not consume significant amounts of processing and timing overhead from the AP. Frequent scheduling of uplink SDMA may lead to poor efficiency in the operation of the AP if only few STAs participate in each uplink transmission.
Consequently, it would be desirable to address one or more of the deficiencies described above.